Keying devices, particularly for electrical musical instruments



Nov. 14, 1967 3 A. MICHEL 3,353,030

. KEYING DEVICES, PARTICULARLY FOR ELECTRICAL -MUSICAL INSTRUMENTS Original Filed Dec. l4 1961 Q INVENTOR Z AoaLF MICHEL.

- B WHZl/M ATTORNEY-5' United States Patent 3,353,030 KEYING DEVRCES, PARTICULARLY FOR ELECTRHIAL MUSICAL ENSTRUMENTS Adolf Michel, 2 Dietramszellerstrasse, Munich 25, Germany Continuation of application Ser. No. 159,244, Dec. 14, 1961. This application Aug. 17, 1966, Ser. No. 573,126 Claims priority, application Germany, Jan. 13, 1961, M 47,686 6 Claims. (Cl. 307-88) ABSTRACT OF THE DISCLOSURE In an electronic musical instrument having an input circuit and an output circuit for conducting electronic musical instrument signals, the improvement comprising means for achieving a high keying ratio between said circuits comprising:

(a) A plurality of transformers connected in tandem between said circuits;

(b) Said transformers having highly permeable cores adapted to degrees of saturation for determining the de gree of isolation between said circuits and the conductance of said output circuit;

(0) Magnetic poles adapted to be moved into proximity with said cores to saturate said transformers and to be moved out of said proximity; and

(d) Means for moving said magnetic poles into and out of said proximity comprising musical instrument keys having a released position for moving said magnetic poles into said proximity and a depressed position for moving said magnetic poles out of said proximity.

Cross-references to related applications The present application is a continuation of application Ser. No. 159,244, filed Dec. 14, 1961, now abandoned.

Applicant claims priority under 35 U.S.C. 119 for German application M 47,686, filed an. 13, 1961.

In electrical musical instruments of the keyed type it is common practice to have each key actuate one or more contacts so that the signals selected by the musician by playing the keys are passed to an output circuit. Since electrical contacts, customarily used, require a certain amount of maintenance and produce signal transients, which are usually not desirable, there has been a very considerable interest in schemes which operate to key selected signals, but in which contacts are not used. In my earlier German patent application M 47,075, and counterparts thereof filed in the United States, Great Britain, Canada, Japan, France and italy, I have described a system which obviates much of the difiiculties. In that system the coupling between input and output circuits is changed at the same time that the impedance of at least the output circuit is changed. In that system it is preferred in most instances to use an associated electrical contact which produces a complete discontinuity in the circuit when the key is in the unactuated condition, although some exceptions are shown.

The principal object of the present invention is to provide a novel keying system in which no contacts are necessary and which is an improvement over the system of the referred to previously filed applications.

Other objects and advantages will become apparent from the following description of a preferred embodiment of the invention.

In the drawings:

FIGS. 1 to inclusive are diagrammatic representations of various related systems, which serve to illustrate the invention.

The demands upon a contactless keying system are very severe, particularly when a large number of keying devices feed into the same output circuit.

Although no precisely measured results have been published concerning loudness distinctions using mixed frequencies (see R. Feldkeller and E. Zwicker, The Ear as an Information Receiver, pp. 76 et seq, S. Hirzel, publisher, Stuttgart, 1956), it can still be said that the overall loudness level is equal to an average value obtained by addition of all the single frequency amplitudes or single frequency power levels of all component frequencies. If then, in the most unfavorable case, a situation is assumed in which direct addition of amplitudes applies, and 100 keying devices are permanently connected to the input of an amplifier, and a noise level of 40 db (1: 100 of the signal level) is desired, it becomes necessary for each individual keying device to provide a 80 db (1:l0,000) signal keying ratio.

A simple solution by which this signal keying ratio can be increased as desired, is the use of a considerable number of variable transformer type coupling devices connected in tandem, of the type described in the foregoing basic patent application. This system is illustrated in FIG. 1. The signal from the generator or signal source T is connected through a decoupling resistor R to an input coil wound upon a small toroid core. This toroid is formed preferably of sintered iron or the equivalent, and is characterized by having a high permeability. A secondary coil wound upon the toroid is connected in turn to the primary coil of a second transformer which may be considered as substantially identical to the first, the output coil of this second transformer being connected to the output circuit V. As illustrated in the drawings, the first transformer is indicated by the designation K whereas the second bears the designation K It will be understood that any desired number of intermediate transformers may be used in the cascade between K and K Because of the high permeability of the toroid cores, the coupling between the input and output circuits has high efficiency. This is the condition shown in the drawings and represents the condition existing when a playing key is depressed. When the playing key is released, one or more small movable permanent magnets indicated by the oblique arrows are brought into close adjacency with the toroid cores so as to produce saturation of the cores. Under these conditions, the input and output circuits are decoupled and the impedance of the circuits is greatly decreased. The ultimate effectconsidering one of the transformers, K for instance-is that when the key is released, not only is the input signal decoupled from the output circuit to a high degree, but also the impedance of the output circuit is greatly decreased so that signals from other sources passing through the output coil will be 0 substantially unimpeded, as when a number of the output coils representing different signal sources are connected in series for instance. It will be appreciated, of course, that the magnet referred to (which may be either a permanent magnet which is movable into or out of association with the toroid, or an electromagnet which is adjacent the toroid and which can be energized to produce saturation) can be under the control of a playing key, or the device may be a portion of a switching circuit controlled in some other manner, as by a stop tab on an organ, for instance.

The scheme so far described, in so far as use is made of the transformer K1 in a switching circuit, is essentially the arrangement of the above referred to previously filed patent application. As indicated above, the signal keying ratio can be increased by using several of the transformers K K in cascade in the manner shown, so that ultimately almost any keying ratio can be achieved.

In FIG. 2 the arrangement of FIG. 1 is elaborated by the inclusion of an additional intermediate impedance de: vice Z which, as shown, may be in the form of a highly permeable toroid having a coil thereon in series with the output coil of transformer K and the input coil of the next transformer in the cascade. If desired, one of these intermediate impedances Z may be connected in circuit with each set of connected input and output transformer coils K These additional impedances Z form a large portion of the total impedance in the circuit between the pairs of input and output coils under conditions where the cores of the transformers K K are saturated, although the additional impedance introduced into the circuit is small when the coupling through the transformers is high.

The effect of this intermediate impedance device can be increased by controlling its impedance also, as is shown in FIG. 3. Here the system is essentially the same as FIG. 2, except that the arrangement is such that when permanent magnets or other devices saturate the cores of coupling transformers K K so as to reduce the impedance of the input and output coils, While at the same time decoupling the transformer secondaries from their primaries, a magnet, or whatever means is used, is so operated as to reduce the saturation of the core of the impedance device Z, thereby placing this device in the high impedance condition. When the key is depressed so as to reduce the saturation of the cores of transformers K K so as to produce a high order of coupling, the core of Z is brought into a condition of saturation so as to reduce the im pedance of this element. The device therefore acts much as does the system of FIG. 2 when the circuit through the coupling elements K K is decoupled, but the impedance of the circuit is reduced to essentially that of FIG. 1 when the signal is coupled through the transformers K -K It will be appreciated that the same permanent magnet can be arranged to move between a position adjacent the cores of K -K when the key is released, to a position away from K K and adjacent the core of the impedance device Z when the key is depressed.

If, however, for purpose of simplifying the construction, for instance, it is desired to change only one coupling member K, or one intermediate impedance device Z, per keying element, the arrangement of FIG. 4 may be used. In this circuit the signal source T is connected to a coil which is common to the toroidal cores of transformers K and K These toroids have separate secondaries connected in series and to the output circuit, with the intermediate impedance element Z being connected across the output. This arrangement provides a bridge circuit which includes coils K and K in which a change of coupling and a change of impedance is achieved by a change in the saturation of only one of the cores of the coupled elements K -K In the blocked or uncoupled condition of the keying device the impedance of the winding Z is arranged to be low, thus short circuiting the high impedance at K and K In the unblocked condition, the impedances of the windings Z and K are high and that of K is low.

This arrangement, besides possessing the capability of increasing the keying ratio by balancing and unbalancing the bridge, also possesses the feature that the input impedance changes only by a factor of two, so that a separate decoupling resistor R is not necessary in most cases.

The FIG. 5 system is much like that of FIG. 4, except that separate primary transformer coils are used, and in addition, the primary and secondary windings of K are reversed with respect to K so that the turns ratio u for K corresponds to a ratio of 1/ u. for K For clarification purposes, the differences of the two bridge circuits are set forth below, as they are employed in the keying devices of FIG. 4 and FIG. 5. Let:

Eg=output voltage of oscillator T E =input voltage of amplifier V u=W /W =turns ratio (for elements K and K in the bridge of FIG. 4; for element K of the bridge of FIG. 5)

1/ u=turns ratio for element K of the bridge of FIG. 5 K=inequality factor of elements K and K Then:

Note 1.Voltage E, is divided between the primary windings of K and K in the ratio l/zfi. Therefore the secondary voltage is:

14 5; u T01 I( .Eg 1-' +u -Et"l+u This means that an additional benefit is achieved when:

JZ J u W1 1 While I have shown and described particular embodiments of my invention, it will be apparent to those skilled in the art that numerous modifications and variations may be made without departing from the underlying principles I of the invention. I therefore desire, by the following claims, to include within the scope of the invention all such modifications and variations by which substantially the results thereof may be obtained by substantially the same or equivalent means.

What is claimed is:

1. In an electronic musical instrument having an input circuit and an output circuit for conducting electronic musical instrument signals, the improvement comprising means for achieving a high keying ratio between said circuits comprising:

(a) a plurality of transformers connected in tandem between said circuits;

(b) said transformers having highly permeable cores adapted to degrees of saturation for determining the degree of isolation between said circuits and the conductance of said output circuit;

(c) magnetic poles adapted to be moved into proximity with said cores to saturate said transformers and to be moved out of said proximity; and

(d) means for moving said magnetic poles into and out of said proximity comprising musical instrument keys having a released position for moving said magnetic poles into said proximity and a depressed position for moving said magnetic poles out of said proximity.

2. The device of claim 1, in which the magnetic poles are parts of a permanent magnet that is movable toward or from the transformer cores.

3. The device of claim 1, in which an additional inductance is connected in series with the secondary of one transformer and the primary of the next following transformer.

4. The device of claim 1, wherein said highly permeable cores comprise sintered iron.

5. A device for achieving a high keying ratio between an input and an output circuit which passes electronic musical instrument signals comprising a plurality of transformers connected between said circuits, said transformers having highly permeable cores the degree of saturation of which determines the degree of isolation movable toward or from the inductive element to vary between the input and the output circuits and also the the saturation thereof. conductance of the output circuit, means including positioned magnets adjacent the transformers to cause the References Cited saturation thereof when keyed for greatly increasing the 5 UNITED STATES PATENTS impedance of the latter when the cores are saturated, but contributing only relatively little increased impedance to 2'781503 2/1957 e the output circuit when the saturation of the cores is low, 2814031 11/1957 Davls 340 174 said means further comprising an inductive element conmeted across the Output circuit. m BERNARD KONICK, Primary Examzner. 6. The device of claim 5, in combination with a magnet S. M. URYNOWICZ, Assistant Examiner. 

1. IN AN ELECTRONIC MUSICAL INSTRUMENT HAVING AN INPUT CIRCUIT AND AN OUTPUT CIRCUIT FOR CONDUCTING ELECTRONIC MUSICAL INSTRUMENT SIGNALS, THE IMPROVEMENT COMPRISING MEANS FOR ACHIEVING A HIGH KEYING RATIO BETWEEN SAID CIRCUITS COMPRISING: (A) A PLURALITY OF TRANSFORMERS CONNECTED IN TANDEM BETWEEN SAID CIRCUITS; (B) SAID TRANSFORMERS HAVING HIGHLY PERMEABLE CORES ADAPTED TO DEGREES OF SATURATION FOR DETERMINING THE DEGREE OF ISOLATION BETWEEN SAID CIRCUIT; CONDUCTANCE OF SAID OUTPUT CIRCUIT; (C) MAGNETIC POLES ADAPTED TO BE MOVED INTO PROXIMITY WITH SAID CORES TO SATURATE SAID TRANSFORMERS AND TO BE MOVED OUT OF SAID PROXIMITY; AND (D) MEANS FOR MOVING SAID MAGNETIC POLES INTO AND OUT OF SAID PROXIMITY COMPRISING MUSICAL INSTRUMENT KEYS HAVING A RELEASED POSITION FOR MOVING SAID MAGNETIC POLES INTO SAID PROXIMITY AND A DEPRESSED POSITION FOR MOVING SAID MAGNETIC POLES OUT OF SAID PROXIMITY. 